1. Field of the Invention
Aspects of the present invention relates to a photo sensing device, a photo sensing circuit, a touch panel, and a method of sensing an output value of a photo sensing element, whereby the influence of a threshold voltage of a driving transistor is removed.
2. Description of the Related Art
Photo sensing devices are used in various ways in order to detect the presence of incident light and the intensity of a spot of incident light. In particular, photo sensing devices have been recently used in order to recognize a touch position of a photo sensing touch screen.
To achieve this, a photo sensing device uses various photo sensing elements, in particular, photo diodes. Each photo diode generates a current in proportion to the intensity of incident light.
A photo sensing device uses a predetermined driving device or element in order to obtain a current generated due to incident light as an output signal. Generally, a driving transistor operating as a source follower is used as a photo sensing device. In order to turn-on a transistor, a voltage greater than a threshold voltage needs to be applied between a gate terminal and a source terminal. At this time, an output of the transistor can be affected by the threshold voltage. In addition, the threshold voltage can vary according to environmental factors such as temperature, electric field, etc.
Along with the development of small-sized and highly-integrated electronic devices, a photo sensing device having maximum sensitivity in a minimized area is desired.